268 . MtTLLEKIAN AND WOLFFIAN DUCTS. 



ventral portion split off from the segmental duct, instead of 

 being as in the female larger in front than the Wolffian duct, is 

 very much smaller ; while behind it does not form a continuous 

 duct, but in some parts a lumen is present, and in others again 

 absent (PL XX. fig. 6). It does not even form an unbroken 

 cord, but is divided in disconnected portions. Those parts 

 with a lumen do not appear to open into the Wolffian duct. 



The process of splitting extends gradually backwards, so that 

 there is a much longer rudimentary Miillerian duct by stage O 

 than by stage N. By stage P the posterior portions of the 

 Miillerian ducts have vanished. The anterior parts remain, 

 as has been already stated, till adult life. A second differ- 

 ence between the male and female depends on the fact 

 that, in the male, the splitting of the segmental duct into 

 Miillerian duct and Wolffian duct never extends beyond the 

 hinder extremity of the small intestine. A third and rather 

 important point of difference consists in the splitting com- 

 mencing far nearer the front end of the segmental duct in the 

 male than in the female. In the female it was shewn that 

 about 48 sections intervened between the front end of the 

 segmental duct and the point where this became split, and that 

 this reo^ion included five or six sesfmental tubes. In the male 

 the homologous space only occupies about 7 to 12 sections, and 

 does not contain the rudiment of more than a single segmental 

 tid)e. Although my sections have not an absolutely uniform 

 thickness, yet the above figures suffice to shew in a conclusive 

 manner that the splitting of the segmental duct commences far 

 further forwards in the male than in the female. This difference 

 accounts for two facts which were mentioned in connection with 

 the excretory organs of the adult, viz. (1) the greater length of 

 the Wolffian body in the male than in the female, and (2) the 

 fact that although a nearly similar number of segmental tubes 

 persist in the adults of both sexes, yet that in the male there 

 are five or six more segments in front of the first fully deve- 

 loped segmental opening than in the female. 



The above description of the formation of the Miillerian duct 

 in the male agrees very closely with that of Professor Semper 

 for Acanthias. For Scyllium however he denies, as it appears 

 to me erroneously, the existence of the posterior rudimentary 



